[PATCH] D58248: [EarlyCSE & MSSA] Cap the clobbering calls in EarlyCSE.

[George Burgess IV via Phabricator via llvm-commits]

george.burgess.iv accepted this revision.
george.burgess.iv marked an inline comment as done.
george.burgess.iv added a comment.
This revision is now accepted and ready to land.

Thanks again!



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Comment at: lib/Transforms/Scalar/EarlyCSE.cpp:1206
   // Reset the current generation.
   CurrentGeneration = LiveOutGeneration;
 
----------------
asbirlea wrote:
> george.burgess.iv wrote:
> > asbirlea wrote:
> > > george.burgess.iv wrote:
> > > > Should we be resetting `ClobberCounter` here, as well?
> > > AFAICT `run()` is only invoked once for an EarlyCSE instance and it's not recursive.
> > > 
> > > I'm also missing the purpose of `CurrentGeneration = LiveOutGeneration;` and
> > > the above
> > > ```
> > >   // Save the current generation.
> > >   unsigned LiveOutGeneration = CurrentGeneration;
> > > ```
> > > Could you please clarify?
> > > AFAICT run() is only invoked once for an EarlyCSE instance and it's not recursive.
> > 
> > That's what I thought, too, but I saw this, so I assumed I was missing something.
> > 
> > Looks like that was added circa 2012; I assume this pass has changed quite a lot since then. I'm hoping davide (or one of the subscribers) may have context on EarlyCSE's usage patterns?
> > 
> > If no one is sure, I vote that we replace it with an early `assert(!CurrentGeneration && "Create a new EarlyCSE instance to run it again")` (which can optionally be removed if no one complains within a reasonable amount of time). 
> I agree with cleaning up existing code, but I will argue against doing it in this patch. Happy to send a follow up one adding the assert.
IMO, if we're not asserting that this 'cleanup' code is useless as a part of this patch, we should be cleaning up the MSSA counter until those assertions do land.

Not a strong enough nit for me to block this patch on, since I agree that it's probably a nop in any case. Your call. :)


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